Trimethoprim sulfamethoxazole

The antibiotic susceptibility profile of the isolates was identified using the standard disk diffusion method on Mueller–Hinton agar (bioMérieux, Marcy l’Etoile, France). Sixteen different antibiotics were tested, including amoxicillin (20 μg), amoxicillin-clavulanic acid (20/10 μg), piperacillin-tazobactam (30/6 μg), cephalotin (30 μg), ceftriaxone (30 μg), cefepime (30 μg), ertapenem (10 μg), imipenem (10 μg), amikacin (30 μg), gentamicin (10 μg), ciprofloxacin (5 μg), Fosfomycin (200 μg), nitrofurantoin (100 μg), tobramycin (10 μg), trimethoprim-sulfamethoxazole (1.25/23.75 μg), and colistin (10 μg) (bioMérieux, Marcy l’Etoile, France). The minimal inhibitory concentration (MIC) of colistin, ertapenem, and imipenem was identified using the microdilution and the E-test methods, respectively. Each strain was considered to be resistant to colistin, ertapenem, and imipenem if their MICs were greater than 2 mg/L, 1 mg/L, and 8 mg/L, respectively. The results were interpreted according to the European Microbial Medical Sensitivity Committee (EUCAST) 2017 (http://www.Sfmicrobiology.Org/Userfiles/Files/Files/CASFM/CASF%20V2_0_MAI2017.PDF, accessed on 25 September 2020).

Antibiotics used for broth microdilution assays (ampicillin, azithromycin, cefazolin, cefoxitin, ceftazidime, ceftriaxone, cephalothin, ciprofloxacin, clarithromycin, enrofloxacin, gentamicin, imipenem, levofloxacin, nalidixic acid, and tetracycline powders) were purchased from the Sigma Chemical Company (St. Louis, MO). Amoxicillin-clavulanic acid and trimethoprim-sulfamethoxazole were obtained as E-test strips from bioMerieux (Durham, NC.). Disks of ampicillin (10 μg), cephalothin (30 μg), enrofloxacin (5 μg), nalidixic acid (30 μg), tetracycline (30 μg), amoxicillin-clavulanic acid (30 μg), and trimethoprim-sulfamethoxazole (25 μg) were obtained from Remel (Lenexa, KS.).

From the soil extract obtained in saline solution (NaCl 0.45%), it was verified that the density of viable microorganisms was >10⁸ ufc mL⁻¹ (optical density [OD] = 0.5 McFarland). The bacterial extraction was sown in Mueller–Hinton agar (Condalab^®, Madrid, Spain), and the minimum inhibitory concentration (MIC) was evaluated by the Kirby–Bauer method, using ε-test antibiotic strips, in triplicate, for the following antibiotics: cefuroxime, cefuroxime axetil, cefoxitin, cefotaxime, ceftazidime, cefepime, ertapenem, imipenem, amikacin, gentamicin, nalidixic acid, ciprofloxacin, tigecycline and trimethoprim/sulfamethoxazole (BioMérieux^®, Marcy l’Etoile, France). Plates were then incubated according to the manufacturer’s instructions. For the quantification of the MIC, the most restrictive halo was used as reference.